A conventional path control technique for a network has following problems: (a) it is impossible to detect routes being congested, in advance; (b) symmetric routing in uplink and downlink cannot be forcibly carried out; (c) it is impossible to reflect the state of a server in routing; (d) it requires a load and/or time to check the states of routes; and (e) it requires a load and/or time to carry out a dynamic processing. Especially, because the Internet, which has come into wide use in recent years, has developed without considering the entire efficiency improvement, it has a lot of problems in efficiency. For example, as for the routing and switching, because autonomous operations are assumed, the protocol is complicated, and there are a lot of cases in which the state in the network is unknown.
For example, JP-A-2001-69146 discloses a technique, whose load for a packet switched network is light, to measure a free bandwidth of a desired section. Specifically, plural test packets are transmitted via one route for each node to two transmission target nodes positioned at both ends of a section to be measured from a measurement apparatus, respectively, to measure packet transfer delay time up to each of the two transmission target nodes. Then, the minimum value and an average value of the measured values are calculated, and from those, a sum of average waiting times in a queue of each node through which packets pass from the measurement apparatus to the transmission target nodes is calculated. Further, from a difference between the sums of the average waiting times, which are obtained for the respective two transmission target nodes, an average section waiting time in a queue to the section to be measured is calculated. Finally, a queue model of the section to be measured is formed, and based on the average section waiting time, a calculation using the queue model is carried out to obtain the free bandwidth. Such a method of transmitting test packets and measuring the delay time is not always effective, because there is still a measurement load.